This invention relates generally to joints for pipe of polymeric material and more particularly to such pipe joints which are used to change or provide an alternate direction of flow through the pipe.
The formation of joints in pipes presents several well-known problems, including the problem of weakness at the joint. The lack of strength may arise, among other reasons, because of the lack of an adequate surface on which to make the connection between the pipes being joined. A smaller diameter branch pipe coming off of a straight section of larger diameter main pipe which is approximately perpendicular to the longitudinal axis of the larger pipe (commonly known as a "reduced T"), presents a particular problem in providing an adequate joint. Presently, the joint between the branch pipe and main pipe is formed by cutting a V-shaped section out of the main pipe, and cutting one end of the branch pipe to a mating V shape sized for reception in the V-shaped opening in the main pipe. Connection of the branch pipe to the main pipe is achieved by welding the side wall of the branch pipe to the side wall of the main pipe. The side wall weld connection is much weaker than the joint connection between adjacent coaxial pipes.
It is also well known that pipes are subject to wear at locations where the pipe changes direction, particularly in applications where the material transported in the pipe is abrasive. Changes in direction are typically achieved by connection of a joint, which is curved or angled, between two pipe sections which are straight. Thus, the excessive wear occurs at the joint. It is known to reinforce the joint by adding additional thickness to the pipe in the joint. However, when the thickness is added on the interior of the pipe (e.g., by a liner) the internal cross section of the pipe is reduced causing an impediment to flow through the joint. The cost of producing special joints having increased thickness is substantial. It is not cost effective to produce a relatively small amount of pipe of increased thickness solely for the purpose of forming the joint.